Daniel Murphy after his first-inning grand slam put the Nationals ahead to stay against the Mets, his former team.CreditCreditJim McIsaac/Getty Images

By Wallace Matthews

April 24, 2017

If the National League East is a two-horse race this season, then right now the Washington Nationals are Secretariat, and the Mets are Sham.

The Mets have not quite dropped more than 30 lengths off the pace, as Sham did behind Secretariat in their 1973 Belmont Stakes matchup, but being five and a half games behind the team they were expected to challenge for the division title, when it is not yet the end of April, seems almost as insurmountable.

The Mets fell, 6-3, Sunday night at Citi Field, completing a sweep by the Nationals, their first at the Mets’ home ballpark since August 2014. The loss was the Mets’ 15th in the last 22 games between the clubs, including 12 of 19 last year. Of their last 37 games at home against the Nationals, the Mets have lost 27 times.

The loss was also the Mets’ eighth in nine games, and their fifth in the first six matchups of their current nine-game homestand, which continues Tuesday when the Atlanta Braves come to town for three games. The Mets are battered and bruised, their lineup depleted by injuries to Yoenis Cespedes, their most dangerous hitter; Lucas Duda, their starting first baseman; and catcher Travis d’Arnaud.

And the news only gets worse this weekend, when they travel to Washington for three more games against the Nationals.

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Michael Conforto’s three hits for the Mets included a single in the fifth inning. He also hit a home run in the first and a single in the third.CreditJim Mcisaac/Getty Images

Still, second baseman Neil Walker, one of the few Mets who did any damage to Nationals starter Max Scherzer on Sunday night, said: “Nobody’s freaking out in here. People may be freaking outside of here, but that’s not any of our concern.”

No, the Mets’ concerns, as enumerated by Manager Terry Collins, are as follows: Get healthy. Start hitting. Resume winning.

“Once we get healthy and get our lineup back in there, I think things will turn around,” said Collins, who received a bit of good news during the game when Cespedes, out since Thursday with a hamstring problem, reported that he was capable of pinch-hitting in the ninth inning.

“If we had gotten one more runner on, he was going up there,” Collins said.

But the Mets never got a chance to send the tying run to the plate; Jose Reyes, who singled in his first at-bat but remains mired at .104, popped out to end the game with a runner at first.

The fact that the outcome of the game was still somewhat in question was thanks to Zack Wheeler, who in only his fourth start after missing two years following Tommy John surgery in March 2015, weathered a rocky first inning to work seven innings and leave with his team trailing by just a run, 4-3.

But some big damage was done to him and the Mets by Daniel Murphy, their former second baseman, who was allowed to leave as a free agent just months after almost single-handedly propelling them into the 2015 World Series with a most-valuable-player performance in the N.L. Championship Series against the Chicago Cubs.

After Wheeler loaded the bases on a hit batter and two singles, Murphy lined a 1-0 fastball over the right-center-field fence for his second career grand slam, giving the Nationals a 4-0 lead with the game less than 10 minutes old.

“Murph’s a great hitter,” Wheeler said. “I tried to throw a fastball past him, but I didn’t get it in enough. I threw it right in his swing path, and he made me pay for it.”

With the former Cy Young Award winner Max Scherzer, who had no-hit the Mets in October 2015, starting for Washington, it seemed as if the Nationals had more than cushion enough already. But a solo home run by Michael Conforto leading off the bottom of the first and a two-run shot by Walker in the third made it a close game, until Josh Smoker surrendered a two-run homer by Ryan Zimmerman in the eighth.

Scherzer settled in to work eight innings, allowing just one more hit after Walker’s home run, a single by Conforto, who had three of the Mets’ hits.

“Any time we play these guys it’s a big series,” Wheeler said. “We know it’s going to be tough throughout the year if we don’t win against these guys.”

The imminent return of Cespedes, who told Collins after the game that he would be ready to return to action on Tuesday, will add some punch to a lineup that lives, and sometimes dies, by the home run. Duda, out with a hyperextended elbow, said he would need every bit of 10 days to return to action, but d’Arnaud, who sustained a bruised right wrist that has made throwing painful, felt well enough to pinch-hit in the eighth, although he struck out.

“Any time someone comes in here and takes three from us, we’re going to be upset,” Conforto said. “But it is early, and we’re going to be fine. We know we’re getting our horses back soon.”

And maybe that two-horse race the N.L. East was supposed to be will wind up being competitive after all.

A version of this article appears in print on , on Page D5 of the New York edition with the headline: Murphy’s Grand Slam Torments the Mets as the Nationals Cap a Sweep. Order Reprints | Today’s Paper | Subscribe